"You can think of fuses as a bridge that allows current to travel across the circuit. The wire (or other component) in the fuse is designed to tolerate a certain level of current. When the current flowing through the circuit experiences a surge, the wire melts or disintegrates, creating a gap that the current cannot cross. Going back to the bridge metaphor, the bridge has a weight limit. A surge of current is like a really heavy truck that caused the bridge to collapse. Don't worry. The truck was empty, as was the bridge."